Seothyra

Abstract: Seothyra henscheli (Eresidae) is a burrowing spider that lives in the dune sea of the southern Namib Desert, Namibia. Prey capture by these spiders involves a foray from a cool subterranean retreat to the undersurface of a capture web that can be lethally hot. Striking, disentangling and retrieving prey from the capture web typically involves several short trips to the capture web, alternating with retreats to the cool burrow. It has been suggested that this behavior limits the increase of body temperature a spider must experience while working at the hot capture web. We used biophysical models in conjunction with direct observations of prey-capture behavior and distributions of sand temperature to estimate body temperatures experienced by S. henscheli during prey capture. In the circumstances we observed, only the relatively long post-strike retreat from the capture web is important in keeping spiders' body temperatures from exceeding their lethal limits. After the post-strike retreat, shuttling appreciably limits the increase in body temperature of small individuals, but may have little effect on body temperature increase in larger spiders.

Abstract: Several small, dome-like roughly ovate calcitic structures with lobed margins found in Miocene aeolianites of the Namib Desert resemble the clover-leaf shaped roof webs made by extant ‘trapdoor’ spiders of the burrowing genus Seothyra (Araneae, Eresidae). These webs consist of a mat of densely-woven silk with slits around the periphery, which is covered, on its upper surface, by sand. The fossils indicate that the genus Seothyra or a similar form of spider, has inhabited the Namib since the Miocene period, and that the capture ecology of the Seothyra type is an ancient one.